The study of nearly all forms of life has two branches, the investigation of living objects, and the similar investigation and classification of fossil specimens. Thus the study of fishes embraces not only the examination of those species now to be found in the waters of the world, but of the fossil fish found whole or in parts, in the treasure-house of the rocks, and these fossil fish have very numerous varieties. Botany also regards not only plants now growing, but the varieties which have become extinct, during the five earlier earth-building periods. Of the ten orders into which it is common among scientists to divide reptiles, five are now extinct, and remain to us only as fossils. But so learned and accurate do some ardent students of fossil remains become, that from only a single bone, tooth, or scale, they are able to decide to what class and family the creature of which it was a part belonged, provided, of course, that the creature itself has become known. No ancient creature seems to have accommodated itself more closely to its circumstances than the reptile. It appeared to be equally at home in the water, on land, or in the air; it ate fish, flesh, and vegetables; walked on two legs, or crawled on four. The biped land reptile had many of the characteristics of the present kangaroo; the bat reptile had many of the qualities of a bird; and the sea reptile was probably more like a whale than a fish. In fact the reptile seems to have been as complaisant as Polonius the courtier-friend of Prince Hamlet in Shakespeare’s play. Let us now write out a little table for reference, showing the improving scale of life in plants and animals, from their first appearance until the reptiles came. ANIMALS. Amoeba. Foraminifera. Crustaceans. Polyps. Mollusks. Fishes. Amphibia. Reptiles. Crinoids. Spiders. Scorpions. Dragon-flies. Cockroaches. Kangaroo-rats. PLANTS. Sea-weeds. Mosses. Ferns. Reeds. Pines. Cycads. The amphibia and reptiles brought into the world not only those famous backbones, but lungs and noses. The amphibia had at first gills and lung-sacs, but the reptiles had true lungs and drew air through their nostrils. Try it: draw in your breath and fill your lungs until your chest rises and expands; now breathe it forth again. Very simple that, do you say? So it seems; it is very common now-a-days, but there were many ages when not a living creature had a pair of lungs and a pair of nostrils, when such breathing apparatus would have been a marvellous affair. These reptiles introduced a brand-new fashion.